Weather Service Report


587 
FXUS66 KPQR 172252
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR 
252 PM PST WED DEC 17 2014

.SYNOPSIS...WEAK LOW PRESSURE WILL CROSS THE AREA THIS EVENING WITH 
SHOWERS LINGERING OVERNIGHT. EXPECT FAIRLY QUIET WEATHER TO START 
THE DAY THURSDAY. A MORE ORGANIZED FRONT WILL BRING GUSTY WINDS TO 
THE COAST WITH RAIN SPREADING INLAND THURSDAY NIGHT AND FRIDAY. 
RISING SNOW LEVELS WILL LIMIT SNOW TO THE HIGHEST PEAKS. COLDER AIR 
BEHIND THE FRONT WILL BRING ACCUMULATING SNOW SHOWERS FOR THE 
CASCADES PASSES FRIDAY EVENING AND SATURDAY. MILD AND VERY WET 
WEATHER ARRIVED THIS WEEKEND. THERE IS POTENTIAL FOR AN ATMOSPHERIC 
RIVER AND ASSOCIATED HEAVY RAIN TO DEVELOP OVER THE AREA AFFECTING 
RIVERS INTO NEXT WEEK.

&&

.SHORT TERM...TONIGHT THROUGH SATURDAY...A WEAK AND SPLITTING TROUGH 
WILL SEND MOST OF ITS ENERGY SOUTH OF OUR AREA TONIGHT. WILL SEE 
SHOWERS TAPER OFF OVERNIGHT AS HIGH PRESSURE BEGINS A TRANSIT ACROSS 
THE AREA. WILL ALSO SEE CORRESPONDING SNOW LEVELS RISE ABOVE THE 
PASSES AND GENERALLY LIMIT THE AMOUNT OF ACCUMULATIONS. THE RIDGE 
AXIS QUICKLY PASSES EAST BY TOMORROW AFTERNOON LEADING TO A LARGELY 
DRY DAY FOR THE INTERIOR. 

ANOTHER MORE COHESIVE TROUGH AND FRONTAL SYSTEM WILL DIG OFFSHORE 
WITH WARM FRONTAL RAIN TOUCHING THE COAST LATE FRIDAY AFTERNOON WITH 
HEAVIER AMOUNTS BY EARLY FRIDAY EVENING. TIMING COULD BE EARLIER 
DEPENDING ON MODEL OF CHOICE WITH THE GFS PERHAPS A COUPLE HOURS 
FASTER THAN THE ECMWF AND THE NAM SLOWER YET. NAM TYPICALLY DOES NOT 
HANDLE WARM PROCESS RAIN VERY WELL SO AM PUTTING LESS WEIGHT ON IT 
TO START WITH. AS THE RAIN COMES IN...A COASTAL JET DEVELOPS 
BRINGING FAIRLY GUSTY WINDS TO THE COAST AND COAST RANGE BUT NOTHING 
TOO OUT OF THE ORDINARY. NOT ANTICIPATING ANY HIGHLIGHTS BUT 
PROBABLY A RUN OF THE MILL WINDY COASTAL STORM. THE ASSOCIATED COLD 
FRONT COME ASHORE AROUND 12Z FRIDAY MORNING AND CROSSES THE CASCADES 
AROUND 17Z WITH COLDER AIR AND LOWERING SNOW LEVELS WITH AND MORE SO 
BEHIND IT. PRECIPITATION TAPERS OFF AND BECOMES MORE SHOWERY IN 
NATURE BEHIND THE FRONT. EXPECT LIGHT ACCUMULATING SNOW BEGINS AT 
WILLAMETTE PASS AROUND DAY BREAK AND LOWERS TO NEAR GOVERNMENT PASS 
LATER THAT MORNING. THE SNOW COMES TO BE TOO LITTLE...TOO LATE FOR 
MUCH APPRECIABLE INCREASE IN THE SNOW PACK WITH PERHAPS A FEW INCHES 
AT THE HIGHER PASSES AND LESS THAN AN INCH FOR GOVERNMENT CAMP. 
HIGHER PEAKS COULD SEE UP TO A FOOT...HOWEVER. ANY OF THE MID 
ELEVATION SNOW WILL BE RATHER SHORT-LIVED AS SNOW LEVELS IMMEDIATELY 
BEGIN RISING IN ANTICIPATION OF THE PACIFIC STORM TRACK BECOMING 
CENTERED OVER THE AREA.

MAIN ATTENTION THIS SHIFT HAS BEEN BE PLACED ON THE ATMOSPHERIC 
RIVER EVENT SETTING UP TO AFFECT THE REGION THIS WEEKEND WITH 
IMPACTS LASTING INTO NEXT WEEK. RAW GFS MODEL RUN ACCUMULATED QPF 
AMOUNTS EXCEED 12 INCHES FOR PORTIONS OF THE CASCADES AND 10 INCHES 
FOR THE COAST RANGE ENDING MONDAY MORNING. WILL SEE THE WARM RAINS 
BEGIN AFFECTING THE COAST RANGE SATURDAY MORNING AND PUSH QUICKLY 
INLAND TO THE CASCADES BY SATURDAY AFTERNOON. MOST OF THE HEAVY RAIN 
OCCURS BEGINNING SATURDAY NIGHT. THERE WOULD BE DEEP WESTERLY FLOW 
FROM THE SURFACE UP TO THE JET LEVEL THUS EXPECT THIS COULD BE AN 
IDEAL OROGRAPHIC SITUATION TO EXTRACT A MAXIMUM AMOUNT OF RAIN FROM 
WHATEVER COMES ASHORE. THERE IS GENERAL LARGE SCALE SUPPORT FROM THE 
ECMWF ALBEIT WITH LESS QPF. PAST EXPERIENCE SHOWS FOLLOWING THE 
HIGHER GFS QPF AMOUNTS IS STILL NOT ENOUGH AND THAT REALITY BRINGS 
SIGNIFICANTLY MORE RAIN. ASSUMING THE CURRENT MODEL RUNS STAY 
UNCHANGED IN THE FUTURE...WOULD EXPECT MULTIPLE MAINSTEM RIVERS 
EXCEEDING FLOOD STAGE AS SOON AS SUNDAY EVENING.
 
HAVE ISSUED SOME OUTLOOK PRODUCTS TODAY LOOKING AHEAD TO FLOODING 
POTENTIAL WITH THE CAVEAT THAT MODELS HAVE SHIFTED THE FOCUS FROM 
NORTHERN WASHINGTON/BRITISH COLUMBIA SOUTH TO OUR AREA DURING THE 
PAST 36 HOURS. ADDITIONAL SHIFTING IS EXPECTED AS WELL AS TIMING 
DIFFERENCES. STAY TUNED AS THIS SITUATION EVOLVES OVER TIME. 
/JBONK

.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...MODELS MAINTAIN A 
FLATTENED RIDGE OVER THE EASTERN PACIFIC FOR THE WEEKEND THROUGH 
EARLY NEXT WEEK. WITH A NEARLY ZONAL JET AND ABUNDANT 
MOISTURE...EXPECT PLENTY OF RAINFALL TO CONTINUE THROUGH SUNDAY. ON 
MONDAY AND TUESDAY...SOME WEAK RIDGING MOVES OVER THE REGION BUT 
SHOWERS LIKELY CONTINUE IN THE MOIST ONSHORE FLOW. AN UPPER TROUGH 
DROPS SOUTH OVER THE REGION BY MIDWEEK WITH SOME RATHER COLD AIR AND 
ADDITIONAL PRECIPITATION IN STORE. WHILE STILL SOME SIGNIFICANT 
UNCERTAINTY EXISTS WITH RESPECT TO THE TIMING OF THE PRECIP VS COLD 
AIR AND JUST HOW COLD THE AIR IS...IT DOES APPEAR THAT A SIGNIFICANT 
SURGE OF COLD AIR MAY MOVE INTO THE REGION AND THEREFORE...DECREASED 
TEMPERATURES ACCORDINGLY FOR THE TUE/WED PERIODS ACROSS THE REGION. 
IT DOES APPEAR THAT SNOW LEVELS WILL DROP BELOW PASS LEVELS AT 
LEAST...AND PERHAPS DOWN INTO THE FOOTHILL ELEVATIONS LATER 
WEDNESDAY INTO THURSDAY. GIVEN THE UNCERTAINTY...THOSE PLANNING 
HOLIDAY TRAVEL DURING THIS PERIOD SHOULD MONITOR THE FORECAST.  
CULLEN

&&

.AVIATION...VFR CONDITIONS LIKELY TO CONTINUE THROUGH THIS
AFTERNOON. ONSHORE WINDS THIS EVENING BEHIND THE WEAK LOW MOVING
ONSHORE WILL ALLOW FOR CIGS AND VIS TO LOWER TO IFR TONIGHT WITH
THE DEVELOPMENT OF FOG/LOW STRATUS. THIS SHOULD HOLD ON THROUGH
THURSDAY MORNING...STARTING TO LIFT BACK TOWARD VFR AROUND 15 TO 18Z
THURSDAY AS WINDS START TO INCREASE OUT OF THE SOUTH. VFR WILL
CONTINUE THROUGH THURSDAY AFTERNOON...THOUGH LOW-LEVEL WIND SHEAR
WILL BE A CONCERN AT KTTD AND POSSIBLY KPDX AS 20 KT EASTERLY
WINDS FROM THE GORGE UNDERCUT INCREASING SOUTHERLY WINDS ALOFT.

KPDX AND APPROACHES...VFR CONDITIONS TO PERSIST THIS
EVENING. WEAK WINDS WILL COULD PROMOTE THE DEVELOPMENT OF FOG/LOW
STRATUS AFTER 06Z THURSDAY...DROPPING CIGS AND VIS TO IFR. THIS
SHOULD LIFT BACK TO VFR BY 18Z THURSDAY. -MCCOY

&&

.MARINE...WEAK LOW PRESSURE SYSTEM MOVING NORTHWARD ALONG THE
COAST HAS BROUGHT WINDS UP TO SCA CRITERIA THIS AFTERNOON IN OUR
SOUTHERN WATERS. THIS IS WEAKENING AND MOVING ONSHORE...WHICH
SHOULD ALLOW WINDS TO SUBSIDE FOR A BRIEF PERIOD THIS EVENING.
WINDS WILL BEGIN TO INCREASE ACROSS OUR WATERS THURSDAY MORNING
AHEAD OF A COLD FRONT WHICH WILL MOVE THROUGH OUR WATERS DURING
THE DAY THURSDAY. AHEAD OF THIS FRONT...WINDS LIKELY TO RAMP UP TO
GALE FORCE WITH A COASTAL JET FULLY DEVELOPED BY THURSDAY
EVENING AND PERSIST UNTIL THE FRONT MOVES ONSHORE EARLY FRIDAY
MORNING.

SEAS CURRENTLY AROUND 10-12 FT WILL DROP TO 9 FT LATER THIS
EVENING. SEAS WILL BEGIN TO BUILD AGAIN THURSDAY MORNING AS WINDS
INCREASE AHEAD OF THE COLD FRONT ON THURSDAY. SEAS EXPECTED TO
BUILD TO THE LOW-TO-MIDDLE TEENS THURSDAY EVENING...SUBSIDING TO
10 TO 12 FT EARLY FRIDAY MORNING. A DYNAMIC FETCH APPROACHES EARLY
FRIDAY...BRINGING A LARGE SWELL INTO OUR WATERS. THIS WILL CAUSE
SEAS TO RAPIDLY BUILD FRIDAY MORNING...REACHING 20 FT FRIDAY
EVENING. THE NEXT STRONG FRONT APPROACHES ON SATURDAY...WITH
GALES POSSIBLE...COULD BUILD SEAS ALREADY 15 TO 20 FEET...TO 20
TO 25 FT SATURDAY. -MCCOY

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 4 AM TO 1 PM PST THURSDAY 
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60 NM.

     GALE WARNING FROM 1 PM THURSDAY TO MIDNIGHT PST THURSDAY NIGHT 
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 9 PM PST THIS 
     EVENING FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 1 PM PST THURSDAY FOR 
     COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 4 AM PST THURSDAY.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA    
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON 
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS 
COMMONLY REFERRED TO AS THE FORECAST AREA.

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Western Regional Climate Center, wrcc@dri.edu